(Radiographics. 2001;21:691-704.)
© RSNA, 2001
Three-dimensional CT Angiography of Spontaneous Portosystemic Shunts1
Kevin P. Henseler, MD,
Myron A. Pozniak, MD,
Fred T. Lee, Jr, MD and
Thomas C. Winter, III, MD
1 From the Department of Radiology, University of Wisconsin Hospital and Clinics, 600 Highland Ave, Madison, WI 53792-3252. Recipient of a Certificate of Merit award for a scientific exhibit at the 1999 RSNA scientific assembly. Received March 20, 2000; revision requested June 9 and received August 14; accepted August 16. Address correspondence to M.A.P. (e-mail: mpozniak@facstaff.wisc.edu).
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Abstract
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Spontaneous portosystemic shunts (varices) are a well-known complication of severe liver disease and portal hypertension. Computed tomographic (CT) angiography was used to image the hepatic vasculature of 198 patients with end-stage liver disease in anticipation of liver transplantation. Performance of a delayed acquisition during the portal phase of enhancement enables evaluation of portal and variceal anatomy without the need for an additional injection of contrast material. Three-dimensional (3D) reconstruction of portal-phase CT angiograms enhances the perception of the courses and anatomic relationships of varices. This information is valuable for surgical planning. Common varices include the left gastric vein, short gastric veins, paraumbilical veins, and splenic vein; in cases of more unusual, complex shunts, 3D rendering is indispensable. By precisely demonstrating the courses of varices, CT angiography allows the surgeon to plan the operative approach and determine the need for surgical varix ligation or preoperative interventional embolization.
Index Terms: Computed tomography (CT), angiography, 95.12916 • Computed tomography (CT), three-dimensional, 95.12917 • Hypertension, portal, 957.711 • Liver, cirrhosis, 761.794 • Shunts, portosystemic, 95.711 • Varices, 95.711
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LEARNING OBJECTIVES FOR TEST 3
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After reading this article and taking the test, the reader will be able to:
- List the common portosystemic shunts encountered in patients with portal hypertension.
- Describe the modifications to routine abdominal CT that are needed to maximize the imaging of portosystemic shunts.
- Recognize the appearance of common portosystemic shunts when displayed with 3D display.
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Introduction
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The advent of computed tomographic (CT) angiography and three-dimensional (3D) rendering has allowed performance of a relatively noninvasive, detailed investigation of the abdominal vasculature. The combination of intravenously administered nonionic contrast material, multi–detector array CT assemblies, higher heat capacity x-ray tubes, faster helical rotation times, more powerful computers, and advanced reformation algorithms has led to acceptance of CT angiography as an alternative to conventional angiography.
Use of biphasic CT of the liver to detect hepatocellular carcinoma has become routine in the work-up of patients with cirrhosis. These patients often require surgical intervention or transplantation, which can be complicated by tortuous and unpredictable varices. A simple modification of the biphasic technique, outlined later in this article, allows the radiologist to augment surgical planning by offering preoperative 3D mapping of variceal pathways. Such mapping provides the surgeon with a detailed, understandable, and anatomically precise model of portosystemic shunts that may be encountered during surgery.
Between April 1996 and July 1999, 198 patients at our institution underwent CT angiography with 3D rendering to rule out a primary hepatic neoplasm and define hepatic arterial anatomy in anticipation of liver transplantation. Performing a delayed acquisition during the portal phase of enhancement enabled us to also evaluate portal and variceal anatomy without the need for an additional injection of contrast material. This article reviews our technique of hepatic CT angiography and 3D reformation. Specific topics discussed are portal hypertension, CT angiography and reformation techniques, phase-specific anatomy, portosystemic shunts, and clinical significance. The article demonstrates variceal pathways seen with CT and shows how 3D CT angiography can aid the surgical team in understanding the complex variceal anatomy that may be encountered during laparotomy. Such understanding could reduce the risk of intraoperative bleeding during surgery ranging from simple abdominal procedures to liver transplantation and could increase the confidence with which surgeons can find and ligate or avoid dominant portosystemic shunts.
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Portal Hypertension
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Portal hypertension is defined as a portal venous pressure of greater than 10 mm Hg. Current theories as to the cause of increased pressure seen in portal hypertension suggest two separate mechanisms (1). The more popular "backward" hypothesis suggests that the increased pressure results from a combination of deposition of collagen in the spaces of Disse and hepatocyte swelling, both of which increase the sinusoidal pressure and cause a relative resistance to sinusoidal flow. An alternative theory holds that hemodynamic factors, including intrahepatic endogenous vasoconstrictors and mesenteric vasodilators, increase blood flow and pressure in the portal venous system. It is likely that both mechanisms contribute to the increased portal venous pressure seen in cirrhotic patients.
Patients with increased portal venous pressures can have a reversal of flow in the portal system, changing from hepatopetal (toward the liver) to hepatofugal (away from the liver). This reversal is thought to result from at least two types of intrahepatic arterioportal communications (2). One is through the vasa vasorum (arterioles) supplying the wall of the portal veins. Another communication takes place at the portal triad. This communication occurs because of direct shunting of blood from the hepatic arteries through the capillary system and into the portal vein. Because hepatic arterial pressure (assumed to be 120/80 mm Hg) exceeds portal venous pressure (normally 5–10 mm Hg), the inflow of arterial blood at the sinusoidal level into the portal vein overwhelms portal inflow.
With progressive liver disease, increasing resistance at the hepatic sinusoidal level elevates portal venous pressure and causes the development and enlargement of portosystemic collateral vessels, the most clinically important of which are gastroesophageal varices (Table 1) (3). Up to 30% of patients with portal hypertension have apparent gastroesophageal varices at endoscopy, and bleeding will eventually occur in 30% of these cases (4). Bleeding from esophageal varices is a major cause of death in patients with portal hypertension. The risk of bleeding is associated with varix size and Child class but not with portal venous pressure (5). Other collateral vessels include recanalized paraumbilical veins, which are of special clinical concern to the surgeon considering a large abdominal incision. An anorectal anastomosis through the inferior mesenteric vein can cause symptomatic hemorrhoidal bleeding. Various retroperitoneal shunts can be encountered, including splenorenal, iliolumbar, intercostal, and phrenic vein shunts. These can be difficult to identify intraoperatively, and preoperative knowledge of their presence and course is valuable, since it is advantageous to ligate these varices to prevent steal of blood from the portal vein.
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CT Angiography and Reformation Techniques
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Historical Perspective
The advent of helical CT scanners in the early 1990s allowed use of the CT scanner as a more dynamic tool. One major advance in the use of helical CT was the ability to obtain scans during the arterial phase after a rapid bolus injection of contrast material, allowing CT arteriography. As a result, many centers started to evaluate the use of CT angiography as an alternative to conventional angiography. During this period, several authors reported the use of 3D rendering techniques to enhance the presentation and perception of the arterial vasculature. In the liver, it became apparent that CT angiography could be of use in identification of the arterial supply to the liver prior to transplantation. In addition, it became clear that arterial-phase imaging improved the sensitivity for detection of hepatocellular carcinoma. One of the main advantages of helical CT is the ability to perform both an arterial-phase acquisition and a portal-phase acquisition, as opposed to portal-phase imaging only. We have found that a technique similar to that used to evaluate and project the arterial supply during early bolus imaging can also be applied to the portal phase, yielding important information about the portal venous system, especially spontaneous portosystemic collateral vessels (varices) in patients with portal hypertension.
CT Angiography
The objective of CT angiography is to acquire image data, appropriately timed relative to the rapid intravenous administration of iodinated contrast material, during both the arterial phase and the portal phase. Ideally, the acquisition is performed on a multi–detector array scanner with a high heat capacity tube and subsecond rotation time. However, it can be adequately executed on earlier-generation helical scanners (as in most of the cases in our study). Low- or iso-osmolality contrast material is mandatory due to the rapid rate of injection, which can cause nausea and vomiting when high-osmolality contrast material is used. A 150-mL dose of intravenous contrast material (iohexol 300 [Omnipaque; Nycomed Amersham, Princeton, NJ]) is administered at a rate of 5 mL/sec, followed by 50 mL of saline solution. This high rate is necessary to achieve a greater intravascular concentration and therefore a higher CT attenuation. Since aberrant hepatic arteries can be relatively small, they need to be sufficiently enhanced so that they are not obscured during 3D threshold-based reconstruction.
Patient requirements for CT angiography are as follows: The patient must be able to tolerate intravenous contrast material (ie, no allergy and acceptable renal function). The patient must also be cooperative (ie, oriented and able to suspend respiration for at least 20 seconds). Finally, venous access must be possible, with a large-bore peripheral intravenous catheter (18-gauge preferable) that flushes easily, preferably in the antecubital fossa.
A nonenhanced sequence is performed with relatively wide collimation (10 mm) for localization of the subsequent sequences. It also allows identification of vascular, biliary, or other calcifications. Focal calcifications at the origin of the celiac artery are a sign of celiac artery stenosis. This finding has implications for potential liver transplant recipients.
Approximately 20 seconds after the start of the contrast material injection, an arterial sequence covering the entire liver and proximal superior mesenteric artery is performed. Narrow collimation (2.5–3 mm) is required to provide detailed resolution with less artifact on the reformation images. A hypervascular mass, which indicates possible hepatocellular carcinoma, is best seen with this sequence.
Approximately 60 seconds after the start of the injection, a third sequence is performed from the diaphragm to the midpelvis with 5-mm collimation. The delay is necessary to allow contrast material to optimally enhance the portal system. This sequence allows evaluation of the portal venous anatomy, especially any varices that may be present. The detailed protocol used at our institution (Table 2) is tailored to the GE Medical Systems (Milwaukee, Wis) scanner but can be modified as needed for other systems.
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Table 2. Protocol for Triphasic CT Angiography of the Liver for Evaluation of a Potential Liver Transplant Recipient and Evaluation of Portal Hypertension
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Two-dimensional and 3D Rendering
Image manipulation and reconstruction can be performed on commercially available independent consoles. Threshold-based software techniques allow electronic dissection of selected anatomic structures (Fig 1).
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Figure 1a. Anterior shaded-surface display (SSD) images show the steps involved in rendering a splenorenal varix imaged during the portal phase. IVC = inferior vena cava. (a) The 3D reconstruction process begins with the entire data set of the torso. This data set is the starting point for electronic dissection. (b) The thresholding technique removes structures outside of specified attenuation values. At this stage of reconstruction, all pixels of less than 100 HU have been removed. Electronic selection of the portal vasculature causes those structures not in continuity to be removed. All that remains is the contiguous vessels, enhanced organs, and the skeletal component. (c) Another model is created with the threshold set to a higher level (220 HU), thus isolating the skeletal component of the torso. (d) The skeletal component is then subtracted from the original model (b), thus leaving the major vasculature and the enhanced organs. (e) Careful electronic dissection and further thresholding allow removal of the organs and clutter, thus revealing the targeted anatomy, which is key to the diagnosis. At this point, most cases can be labeled and recorded to the satisfaction of the clinician. (f) If further detail is desired, the process can continue. Additional electronic dissection can separate individual vessels or vascular systems. (g) The vessels can be color encoded to enhance their visibility in the reassembled model. Here, the gonadal vein is encoded yellow, the inferior vena cava is encoded blue, the portal venous system is encoded pink, and the splenomesenteric varix is encoded red. (h) Some or all of the individual components can then be reassembled. Additional anatomic structures can be inserted to serve as reference points. Here, a large inferior mesenteric varix (red area) courses inferiorly from the splenic vein. Eventually, blood flow returns to the systemic circulation via the left gonadal vein (yellow area). The spleen is encoded tan. (i) Finally, to provide a global view of the anatomic relationships, the vascular model can be placed back into the SSD image of the torso (a). The extent and location of the varices is readily perceived by using a transparency model.
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Figure 1b. Anterior shaded-surface display (SSD) images show the steps involved in rendering a splenorenal varix imaged during the portal phase. IVC = inferior vena cava. (a) The 3D reconstruction process begins with the entire data set of the torso. This data set is the starting point for electronic dissection. (b) The thresholding technique removes structures outside of specified attenuation values. At this stage of reconstruction, all pixels of less than 100 HU have been removed. Electronic selection of the portal vasculature causes those structures not in continuity to be removed. All that remains is the contiguous vessels, enhanced organs, and the skeletal component. (c) Another model is created with the threshold set to a higher level (220 HU), thus isolating the skeletal component of the torso. (d) The skeletal component is then subtracted from the original model (b), thus leaving the major vasculature and the enhanced organs. (e) Careful electronic dissection and further thresholding allow removal of the organs and clutter, thus revealing the targeted anatomy, which is key to the diagnosis. At this point, most cases can be labeled and recorded to the satisfaction of the clinician. (f) If further detail is desired, the process can continue. Additional electronic dissection can separate individual vessels or vascular systems. (g) The vessels can be color encoded to enhance their visibility in the reassembled model. Here, the gonadal vein is encoded yellow, the inferior vena cava is encoded blue, the portal venous system is encoded pink, and the splenomesenteric varix is encoded red. (h) Some or all of the individual components can then be reassembled. Additional anatomic structures can be inserted to serve as reference points. Here, a large inferior mesenteric varix (red area) courses inferiorly from the splenic vein. Eventually, blood flow returns to the systemic circulation via the left gonadal vein (yellow area). The spleen is encoded tan. (i) Finally, to provide a global view of the anatomic relationships, the vascular model can be placed back into the SSD image of the torso (a). The extent and location of the varices is readily perceived by using a transparency model.
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Figure 1c. Anterior shaded-surface display (SSD) images show the steps involved in rendering a splenorenal varix imaged during the portal phase. IVC = inferior vena cava. (a) The 3D reconstruction process begins with the entire data set of the torso. This data set is the starting point for electronic dissection. (b) The thresholding technique removes structures outside of specified attenuation values. At this stage of reconstruction, all pixels of less than 100 HU have been removed. Electronic selection of the portal vasculature causes those structures not in continuity to be removed. All that remains is the contiguous vessels, enhanced organs, and the skeletal component. (c) Another model is created with the threshold set to a higher level (220 HU), thus isolating the skeletal component of the torso. (d) The skeletal component is then subtracted from the original model (b), thus leaving the major vasculature and the enhanced organs. (e) Careful electronic dissection and further thresholding allow removal of the organs and clutter, thus revealing the targeted anatomy, which is key to the diagnosis. At this point, most cases can be labeled and recorded to the satisfaction of the clinician. (f) If further detail is desired, the process can continue. Additional electronic dissection can separate individual vessels or vascular systems. (g) The vessels can be color encoded to enhance their visibility in the reassembled model. Here, the gonadal vein is encoded yellow, the inferior vena cava is encoded blue, the portal venous system is encoded pink, and the splenomesenteric varix is encoded red. (h) Some or all of the individual components can then be reassembled. Additional anatomic structures can be inserted to serve as reference points. Here, a large inferior mesenteric varix (red area) courses inferiorly from the splenic vein. Eventually, blood flow returns to the systemic circulation via the left gonadal vein (yellow area). The spleen is encoded tan. (i) Finally, to provide a global view of the anatomic relationships, the vascular model can be placed back into the SSD image of the torso (a). The extent and location of the varices is readily perceived by using a transparency model.
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Figure 1d. Anterior shaded-surface display (SSD) images show the steps involved in rendering a splenorenal varix imaged during the portal phase. IVC = inferior vena cava. (a) The 3D reconstruction process begins with the entire data set of the torso. This data set is the starting point for electronic dissection. (b) The thresholding technique removes structures outside of specified attenuation values. At this stage of reconstruction, all pixels of less than 100 HU have been removed. Electronic selection of the portal vasculature causes those structures not in continuity to be removed. All that remains is the contiguous vessels, enhanced organs, and the skeletal component. (c) Another model is created with the threshold set to a higher level (220 HU), thus isolating the skeletal component of the torso. (d) The skeletal component is then subtracted from the original model (b), thus leaving the major vasculature and the enhanced organs. (e) Careful electronic dissection and further thresholding allow removal of the organs and clutter, thus revealing the targeted anatomy, which is key to the diagnosis. At this point, most cases can be labeled and recorded to the satisfaction of the clinician. (f) If further detail is desired, the process can continue. Additional electronic dissection can separate individual vessels or vascular systems. (g) The vessels can be color encoded to enhance their visibility in the reassembled model. Here, the gonadal vein is encoded yellow, the inferior vena cava is encoded blue, the portal venous system is encoded pink, and the splenomesenteric varix is encoded red. (h) Some or all of the individual components can then be reassembled. Additional anatomic structures can be inserted to serve as reference points. Here, a large inferior mesenteric varix (red area) courses inferiorly from the splenic vein. Eventually, blood flow returns to the systemic circulation via the left gonadal vein (yellow area). The spleen is encoded tan. (i) Finally, to provide a global view of the anatomic relationships, the vascular model can be placed back into the SSD image of the torso (a). The extent and location of the varices is readily perceived by using a transparency model.
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Figure 1e. Anterior shaded-surface display (SSD) images show the steps involved in rendering a splenorenal varix imaged during the portal phase. IVC = inferior vena cava. (a) The 3D reconstruction process begins with the entire data set of the torso. This data set is the starting point for electronic dissection. (b) The thresholding technique removes structures outside of specified attenuation values. At this stage of reconstruction, all pixels of less than 100 HU have been removed. Electronic selection of the portal vasculature causes those structures not in continuity to be removed. All that remains is the contiguous vessels, enhanced organs, and the skeletal component. (c) Another model is created with the threshold set to a higher level (220 HU), thus isolating the skeletal component of the torso. (d) The skeletal component is then subtracted from the original model (b), thus leaving the major vasculature and the enhanced organs. (e) Careful electronic dissection and further thresholding allow removal of the organs and clutter, thus revealing the targeted anatomy, which is key to the diagnosis. At this point, most cases can be labeled and recorded to the satisfaction of the clinician. (f) If further detail is desired, the process can continue. Additional electronic dissection can separate individual vessels or vascular systems. (g) The vessels can be color encoded to enhance their visibility in the reassembled model. Here, the gonadal vein is encoded yellow, the inferior vena cava is encoded blue, the portal venous system is encoded pink, and the splenomesenteric varix is encoded red. (h) Some or all of the individual components can then be reassembled. Additional anatomic structures can be inserted to serve as reference points. Here, a large inferior mesenteric varix (red area) courses inferiorly from the splenic vein. Eventually, blood flow returns to the systemic circulation via the left gonadal vein (yellow area). The spleen is encoded tan. (i) Finally, to provide a global view of the anatomic relationships, the vascular model can be placed back into the SSD image of the torso (a). The extent and location of the varices is readily perceived by using a transparency model.
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Figure 1f. Anterior shaded-surface display (SSD) images show the steps involved in rendering a splenorenal varix imaged during the portal phase. IVC = inferior vena cava. (a) The 3D reconstruction process begins with the entire data set of the torso. This data set is the starting point for electronic dissection. (b) The thresholding technique removes structures outside of specified attenuation values. At this stage of reconstruction, all pixels of less than 100 HU have been removed. Electronic selection of the portal vasculature causes those structures not in continuity to be removed. All that remains is the contiguous vessels, enhanced organs, and the skeletal component. (c) Another model is created with the threshold set to a higher level (220 HU), thus isolating the skeletal component of the torso. (d) The skeletal component is then subtracted from the original model (b), thus leaving the major vasculature and the enhanced organs. (e) Careful electronic dissection and further thresholding allow removal of the organs and clutter, thus revealing the targeted anatomy, which is key to the diagnosis. At this point, most cases can be labeled and recorded to the satisfaction of the clinician. (f) If further detail is desired, the process can continue. Additional electronic dissection can separate individual vessels or vascular systems. (g) The vessels can be color encoded to enhance their visibility in the reassembled model. Here, the gonadal vein is encoded yellow, the inferior vena cava is encoded blue, the portal venous system is encoded pink, and the splenomesenteric varix is encoded red. (h) Some or all of the individual components can then be reassembled. Additional anatomic structures can be inserted to serve as reference points. Here, a large inferior mesenteric varix (red area) courses inferiorly from the splenic vein. Eventually, blood flow returns to the systemic circulation via the left gonadal vein (yellow area). The spleen is encoded tan. (i) Finally, to provide a global view of the anatomic relationships, the vascular model can be placed back into the SSD image of the torso (a). The extent and location of the varices is readily perceived by using a transparency model.
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Figure 1g. Anterior shaded-surface display (SSD) images show the steps involved in rendering a splenorenal varix imaged during the portal phase. IVC = inferior vena cava. (a) The 3D reconstruction process begins with the entire data set of the torso. This data set is the starting point for electronic dissection. (b) The thresholding technique removes structures outside of specified attenuation values. At this stage of reconstruction, all pixels of less than 100 HU have been removed. Electronic selection of the portal vasculature causes those structures not in continuity to be removed. All that remains is the contiguous vessels, enhanced organs, and the skeletal component. (c) Another model is created with the threshold set to a higher level (220 HU), thus isolating the skeletal component of the torso. (d) The skeletal component is then subtracted from the original model (b), thus leaving the major vasculature and the enhanced organs. (e) Careful electronic dissection and further thresholding allow removal of the organs and clutter, thus revealing the targeted anatomy, which is key to the diagnosis. At this point, most cases can be labeled and recorded to the satisfaction of the clinician. (f) If further detail is desired, the process can continue. Additional electronic dissection can separate individual vessels or vascular systems. (g) The vessels can be color encoded to enhance their visibility in the reassembled model. Here, the gonadal vein is encoded yellow, the inferior vena cava is encoded blue, the portal venous system is encoded pink, and the splenomesenteric varix is encoded red. (h) Some or all of the individual components can then be reassembled. Additional anatomic structures can be inserted to serve as reference points. Here, a large inferior mesenteric varix (red area) courses inferiorly from the splenic vein. Eventually, blood flow returns to the systemic circulation via the left gonadal vein (yellow area). The spleen is encoded tan. (i) Finally, to provide a global view of the anatomic relationships, the vascular model can be placed back into the SSD image of the torso (a). The extent and location of the varices is readily perceived by using a transparency model.
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Figure 1h. Anterior shaded-surface display (SSD) images show the steps involved in rendering a splenorenal varix imaged during the portal phase. IVC = inferior vena cava. (a) The 3D reconstruction process begins with the entire data set of the torso. This data set is the starting point for electronic dissection. (b) The thresholding technique removes structures outside of specified attenuation values. At this stage of reconstruction, all pixels of less than 100 HU have been removed. Electronic selection of the portal vasculature causes those structures not in continuity to be removed. All that remains is the contiguous vessels, enhanced organs, and the skeletal component. (c) Another model is created with the threshold set to a higher level (220 HU), thus isolating the skeletal component of the torso. (d) The skeletal component is then subtracted from the original model (b), thus leaving the major vasculature and the enhanced organs. (e) Careful electronic dissection and further thresholding allow removal of the organs and clutter, thus revealing the targeted anatomy, which is key to the diagnosis. At this point, most cases can be labeled and recorded to the satisfaction of the clinician. (f) If further detail is desired, the process can continue. Additional electronic dissection can separate individual vessels or vascular systems. (g) The vessels can be color encoded to enhance their visibility in the reassembled model. Here, the gonadal vein is encoded yellow, the inferior vena cava is encoded blue, the portal venous system is encoded pink, and the splenomesenteric varix is encoded red. (h) Some or all of the individual components can then be reassembled. Additional anatomic structures can be inserted to serve as reference points. Here, a large inferior mesenteric varix (red area) courses inferiorly from the splenic vein. Eventually, blood flow returns to the systemic circulation via the left gonadal vein (yellow area). The spleen is encoded tan. (i) Finally, to provide a global view of the anatomic relationships, the vascular model can be placed back into the SSD image of the torso (a). The extent and location of the varices is readily perceived by using a transparency model.
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Figure 1i. Anterior shaded-surface display (SSD) images show the steps involved in rendering a splenorenal varix imaged during the portal phase. IVC = inferior vena cava. (a) The 3D reconstruction process begins with the entire data set of the torso. This data set is the starting point for electronic dissection. (b) The thresholding technique removes structures outside of specified attenuation values. At this stage of reconstruction, all pixels of less than 100 HU have been removed. Electronic selection of the portal vasculature causes those structures not in continuity to be removed. All that remains is the contiguous vessels, enhanced organs, and the skeletal component. (c) Another model is created with the threshold set to a higher level (220 HU), thus isolating the skeletal component of the torso. (d) The skeletal component is then subtracted from the original model (b), thus leaving the major vasculature and the enhanced organs. (e) Careful electronic dissection and further thresholding allow removal of the organs and clutter, thus revealing the targeted anatomy, which is key to the diagnosis. At this point, most cases can be labeled and recorded to the satisfaction of the clinician. (f) If further detail is desired, the process can continue. Additional electronic dissection can separate individual vessels or vascular systems. (g) The vessels can be color encoded to enhance their visibility in the reassembled model. Here, the gonadal vein is encoded yellow, the inferior vena cava is encoded blue, the portal venous system is encoded pink, and the splenomesenteric varix is encoded red. (h) Some or all of the individual components can then be reassembled. Additional anatomic structures can be inserted to serve as reference points. Here, a large inferior mesenteric varix (red area) courses inferiorly from the splenic vein. Eventually, blood flow returns to the systemic circulation via the left gonadal vein (yellow area). The spleen is encoded tan. (i) Finally, to provide a global view of the anatomic relationships, the vascular model can be placed back into the SSD image of the torso (a). The extent and location of the varices is readily perceived by using a transparency model.
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Data Analysis
Measurement of the diameter and length of the main portal vein is performed on two-dimensional reformation images (Fig 2). These measurements are important for transplantation planning in regard to the portal vein–donor liver anastomosis. Further evaluation of the hepatic vascular anatomy requires 3D rendering because the complex courses of these vessels cannot be adequately studied in two dimensions.
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Figure 2. Two-dimensional reformation image obtained along the long axis of the portal vein shows measurement of the transverse diameter and length of this vessel. This information allows the transplantation surgeon to anticipate an anastomotic size mismatch between the recipient and donor portal veins.
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The 3D reformation images are created to optimize perception and enhance understanding of the anatomy. Separate SSD images are created for the hepatic arterial anatomy and portal venous anatomy, especially the variceal anatomy. For the purposes of this article, we extended the 3D rendering process by adding color to enhance perception of anatomic detail. In daily practice, we liberally annotate but do not color encode the reformation images (Fig 3). In the hands of a skilled operator using state-of-the-art commercially available equipment, the basic rendering can be executed in 3–10 minutes.
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Figure 3. Anterior SSD image shows the portal system with liberal annotation. Such annotation at the time of imaging helps decrease the need for repeat consultation with the clinicians. lt = left, rt = right, smv = superior mesenteric vein.
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Image Display
Source images are photographed, since we are not yet a filmless department. However, only every fourth image from the 2.5-mm collimation arterial-phase sequence and every other image from the 5-mm collimation portal-phase sequence is photographed. Of course, all image data are reviewed on an independent workstation (Advantage Windows Workstation, version 3.1; GE Medical Systems). A sheet of annotated two-dimensional and 3D reformation images is produced to transmit the findings to the surgeons.
An important role of the supervising radiologist is to determine the projections that best show the findings. A few degrees of obliquity can make a substantial difference in the diagnostic value of an image.
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Phase-specific Anatomy
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The data sets acquired during the arterial and portal phases are evaluated individually.
Arterial Phase
Three-dimensional rendering of the arterial-phase data allows reconstruction of the arterial blood supply to the liver. The origin of the celiac artery is evaluated with two-dimensional reformation to rule out stenosis. In the event of transplantation, this evaluation provides the surgeon with important information regarding the planning of the arterial anastomosis. In cases of standard hepatic artery anatomy, the entire liver supply originates from the celiac artery. Any arterial anatomic variant (eg, branches from the left gastric artery or superior mesenteric artery or even rare cases of the entire hepatic supply originating from the superior mesenteric artery) will complicate liver transplantation; such variants can be identified preoperatively.
Portal Phase
Anatomic variants of the portal vein are rare. However, varices are common in portal hypertension, and these are the focus of the remainder of this article. Portal vein thrombosis must be identified in the transplantation candidate (Fig 4).
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Figure 4. Anterior portal-phase SSD image shows blood flow from the superior mesenteric vein (smv) and splenic vein continuing via a large left gastric-esophageal varix. The portal vein is not visible due to thrombosis.
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Mixed
Portal system enhancement during the arterial-phase sequence occurs if there is a delay in initiating arterial-phase scanning. In the rare situation of an arterioportal fistula, both systems may appear markedly enhanced on arterial-phase images (Fig 5). Correlation with the clinical history (eg, complication of liver biopsy, hepatocellular carcinoma, or Osler-Weber-Rendu disease) may allow confirmation of the diagnosis.
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Figure 5. Left lateral oblique arterial-phase SSD image shows the aorta and its major branches (including the hepatic artery) encoded in red. However, the portal system (blue area) is also markedly enhanced. This degree of enhancement of the portal system is inappropriate during the early arterial phase of scanning. The early portal enhancement was secondary to an arteriovenous fistula, which was the sequela of a biopsy.
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Portosystemic Shunts
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Gastroesophageal Varices
The most common and most clinically important portosystemic shunt is through gastroesophageal varices. The blood flow to gastroesophageal varices is predominantly from the left gastric vein (also called the coronary vein) (Fig 6). This vein originates at the portal venous confluence, traverses the gastric fundus, and drains into the veins of the lower esophageal plexus (6). Shunting also occurs from the splenic vein through the short gastric veins and into the esophageal plexus (Fig 7). These varices flow into the deep, intrinsic, longitudinal veins of the lower esophagus, which dilate and are responsible for the bleeding encountered in cases of gastroesophageal varices (7). These veins can increase in size sixfold (Fig 8) and carry up to a half liter of blood per minute (8). This high-volume blood flow accounts for the high mortality associated with spontaneous variceal bleeding. Identification of all the vessels shunting blood to the gastroesophageal varices is important, since it has been demonstrated that there is extensive collateralization throughout this network (7). Therefore, treatment should occlude all large collateral vessels, or significant steal of blood from the portal vein can occur after transplantation.
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Figure 6. Left anterior oblique SSD image shows a large left gastric-esophageal varix that courses cephalically in a patient with end-stage liver disease. At the level of the diaphragm, the varix becomes a tortuous esophageal varix. Standard (non-color-encoded) rendering is sufficient in most such cases. PV = portal vein, SMV = superior mesenteric vein.
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Figure 7. Anterior SSD image shows a large left gastric varix (red area). Numerous short gastric veins (green area) are seen along the greater curvature of the stomach, coursing toward the gastroesophageal junction. The portal, splenic, and superior mesenteric veins are encoded pink. PV = portal vein.
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Figure 8. Right anterior oblique SSD image shows a large left gastric-esophageal varix (blue area) that drains the portal venous circulation (pink area). Superimposition of the color-encoded SSD image onto a transparent torso clearly demonstrates the impressive size of the varix. SMV = superior mesenteric vein, SV = splenic vein.
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With splenic vein thrombosis, collateral flow can course via a gastroepiploic varix through the stomach wall (Fig 9). The result can be variceal bleeding from isolated gastric varices.
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Figure 9. Color-encoded 3D image (superior view) shows a large gastroepiploic varix (blue area) that courses around the greater curvature of the stomach in a patient with a thrombosed splenic vein. Note the tortuosity and markedly increased diameter of the varix, particularly in the region of the gastroesophageal (GE) junction. Branches of the portal vein (PV) and superior mesenteric vein (SMV) are encoded pink.
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Recanalized Paraumbilical Vein
The umbilical vein, which runs in the falciform ligament, atrophies after birth and becomes the ligamentum teres. Coursing through this ligament are additional smaller paraumbilical veins. These veins may hypertrophy in the presence of elevated portal venous pressure and are then known as recanalized paraumbilical veins (varices) (9).
Occasionally, a paraumbilical varix leads to enlargement of the superficial abdominal wall veins, causing the so-called caput medusae (Fig 10). However, caput medusae is a rare consequence of paraumbilical varix. The paraumbilical vein originates from the left portal vein, courses along the falciform ligament, and usually extends toward the umbilicus (Fig 11). The vast majority of paraumbilical flow returns to the systemic circulation via one of the two inferior epigastric veins (Fig 12). Other alternatives are possible, including a cephalic course that communicates via the substernal veins or internal mammary veins with the intercostal and azygos veins.
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Figure 10. Photograph shows a caput medusae accentuated by a large amount of ascites in a patient being prepared for liver transplantation. An extensive plexus of veins is seen emanating from the umbilical region and radiating across the anterior abdominal wall. Note the large vein coursing inferiorly along the right flank (arrows). This is the superficial epigastric vein, which drains into the external iliac vein.
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Figure 11. Three-dimensional image (right inferior view) shows a portal vein-paraumbilical varix (pink area). Portal venous flow courses through the large left portal vein into the paraumbilical varix along the falciform ligament. With the transparent overlay of the torso, the relationship of the varix to the abdominal wall (deep to the linea alba [arrow]) becomes apparent.
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Figure 12. Right lateral SSD image shows the portal venous system and a recanalized paraumbilical vein (pink area). The varix (yellow arrows) courses inferiorly along the anterior abdominal wall past the umbilicus (open white arrow) and continues via the inferior epigastric vein (solid white arrows) to the left external iliac vein and the systemic circulation (blue area). IVC = inferior vena cava.
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In utero, the umbilical vein penetrates the anterior abdominal wall at the umbilicus on its way from the placenta. With recanalization of the paraumbilical veins, which share this course, the varix may appear as an umbilical hernia at physical examination (Fig 13). If it is just deep to the skin, it may be mistaken for herniated intestine at physical examination. This mistake may lead to a bloody surprise for the surgeon expecting todo a simple hernia repair. These hernias can be seen as focal dilatation of the varix at CT angiography (Fig 14) or as a large knot of color just deep to the umbilicus at ultrasonography (US) (Fig 15).
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Figure 14a. Lateral oblique 3D images show a recanalized paraumbilical vein superimposed on a transparency of the torso. (a) The varix (black arrows) courses deep to the anterior abdominal wall and develops a rounded prominence at the umbilicus (yellow arrow). (b) The varix (black arrows) courses toward the umbilicus and has a large herniated component extending just beneath the skin (yellow arrow). However, this varix continues into the superficial epigastric vein (white arrows).
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Figure 14b. Lateral oblique 3D images show a recanalized paraumbilical vein superimposed on a transparency of the torso. (a) The varix (black arrows) courses deep to the anterior abdominal wall and develops a rounded prominence at the umbilicus (yellow arrow). (b) The varix (black arrows) courses toward the umbilicus and has a large herniated component extending just beneath the skin (yellow arrow). However, this varix continues into the superficial epigastric vein (white arrows).
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Figure 15. Longitudinal color Doppler image shows a large knot of vessels just deep to the umbilicus (arrowheads). Flow from the recanalized paraumbilical vein (puv) (white arrows) passes into this herniated component, with outflow via the inferior epigastric vein (iev) (yellow arrows).
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Splenorenal and Retroperitoneal Varices
Common thinking about splenorenal varices is that they originate from the splenic hilum and travel directly to the renal vein. This situation is actually the exception. Most varices in the left flank are convoluted, traveling a great distance before communicating with the systemic circulation and not always communicating directly with the renal vein. Varices originating from the splenic hilar region may course cephalically toward the diaphragm and pass along the diaphragmatic surface posterior or lateral to the spleen, eventually communicating with the renal vein (Figs 16, 17).
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Figure 16a. Splenorenal varix in a patient with portal hypertension. (a) Posterior 3D image shows a varix (red area) (solid arrows), which travels completely around the kidney (yellow area) to eventually reach the left renal vein (open arrow). The spleen is enlarged (tan area). The portal system is encoded magenta. pv = portal vein, smv = superior mesenteric vein. (b) Anterior SSD image with the spleen removed shows the convoluted course of the varix (red area). The kidney is encoded yellow, and the portal system is encoded magenta.
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Figure 16b. Splenorenal varix in a patient with portal hypertension. (a) Posterior 3D image shows a varix (red area) (solid arrows), which travels completely around the kidney (yellow area) to eventually reach the left renal vein (open arrow). The spleen is enlarged (tan area). The portal system is encoded magenta. pv = portal vein, smv = superior mesenteric vein. (b) Anterior SSD image with the spleen removed shows the convoluted course of the varix (red area). The kidney is encoded yellow, and the portal system is encoded magenta.
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Figure 17. Anterior SSD image shows an elongated splenorenal varix (blue area). The varix travels from the splenic hilar region inferiorly along the left flank, down into the pelvis, and eventually back up to the left renal vein (arrow) via the left gonadal vein (lgv). The kidney is encoded yellow, the portal system is encoded magenta, and the spleen is encoded tan.
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Alternatively, the origin of the collateral flow in the left flank may be from the inferior mesenteric vein. This varix usually returns to the systemic circulation via the left gonadal vein (Fig 1h, 1i). Occasionally, flow returns via the right gonadal vein (Fig 18) or ascending lumbar vein (Fig 19).
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Figure 18. Anterior 3D image shows a large portosystemic varix (red area) coursing via the superior mesenteric vein (smv) into a complex knot of vessels in the right lower quadrant (open arrow). From there, flow returns to the inferior vena cava (blue area) via the right gonadal vein (solid arrow).
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Figure 19. Left inferior oblique 3D image shows an inferior mesenteric vein varix (black arrows) coursing toward the pelvis. It returns to the systemic circulation via an enlarged lumbar vein (white arrows) closely apposed to the spine.
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Among the myriad of portosystemic shunts are left gastric–renal shunts (Fig 20). The pathway of this shunt is usually via the suprarenal vein, which becomes markedly dilated and tortuous.
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Figure 20. Left oblique 3D image shows a large portosystemic varix (purple area). It courses via the left gastric vein (arrowheads) to the left suprarenal vein (white arrows) and eventually into the left renal vein (yellow arrow). The inferior vena cava (IVC) is encoded blue, the kidney is encoded yellow, and the spleen is encoded tan.
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Clinical Significance
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The demonstration of variceal anatomy made possible by CT angiography provides a more thorough understanding of the variceal orientation and relationship to adjacent organs. This knowledge can be invaluable to surgeons anticipating difficult procedures in patients who often are already in a clinically tenuous condition. Since portosystemic varices develop by means of distention and elongation of preexisting small veins, variceal walls are thin. These vessels are easily torn and difficult to repair. There have been many reported cases of intraoperative mortality due to accidental disruption of an unexpected varix. When given a choice, surgeons prefer to stay away from a variceal bed.
A midline incision in a patient with portal hypertension may become a bloody misadventure. Even with knowledge of a recanalized paraumbilical vein, the true extent and complexity may be underestimated without explicit information about its course and size (Fig 21). These convoluted varices can interfere with any abdominal surgery, causing unintended complications. A colectomy for diverticulitis can quickly become complicated by inferior mesenteric or paraumbilical varices (Fig 22). Even a simple hernia operation can become difficult if a palpable hernia is assumed to contain viscera but instead contains a herniated paraumbilical varix (Fig 14). Occasionally, laparoscopic surgery can become complicated by encounters with varices. An attempt to remove an adnexal mass can have dire consequences if it is discovered that in actuality the mass is a nest of varices between the inferior mesenteric vein and gonadal vein (Fig 23). Therefore, the addition of portal-phase imaging with 3D vascular reconstruction can be a clinically important adjunct to the information obtained during liver CT.
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Figure 21. Anterosuperior 3D image with a transparent overlay of the torso shows a paraumbilical varix (red area). Note the large plexus of vessels just deep to the anterior abdominal wall (arrows). A surgical incision or even a small laparoscopic puncture may result in significant blood loss.
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Figure 22a. Variceal inferior epigastric vein in a patient who was being evaluated prior to surgery for diverticulitis. (a) Oblique color Doppler image of the left lower quadrant shows a hypoechoic, edematous bowel loop (arrows), which represents the inflamed sigmoid colon. Just superficial to it is a large vascular structure. This is an intervening variceal left inferior epigastric vein. (b) Right anterior oblique 3D image shows the course of the varix (arrows). It eventually communicates with the left external iliac vein (eiv).
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Figure 22b. Variceal inferior epigastric vein in a patient who was being evaluated prior to surgery for diverticulitis. (a) Oblique color Doppler image of the left lower quadrant shows a hypoechoic, edematous bowel loop (arrows), which represents the inflamed sigmoid colon. Just superficial to it is a large vascular structure. This is an intervening variceal left inferior epigastric vein. (b) Right anterior oblique 3D image shows the course of the varix (arrows). It eventually communicates with the left external iliac vein (eiv).
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Figure 23a. Left-sided pelvic varix in a female patient with a palpable pelvic mass at physical examination. (a) Longitudinal US image of the pelvis shows a complex, multiseptated structure (arrows). (b) Longitudinal color Doppler image shows that the lesion is not a cystic neoplasm but a large vascular complex. (c) Coronal magnetic resonance angiogram of the lower abdomen and pelvis shows that the lesion is a left-sided pelvic varix. Portal venous flow courses via the inferior mesenteric vein (IMV) into a complex knot of vessels in the left adnexal region (arrows).
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Figure 23b. Left-sided pelvic varix in a female patient with a palpable pelvic mass at physical examination. (a) Longitudinal US image of the pelvis shows a complex, multiseptated structure (arrows). (b) Longitudinal color Doppler image shows that the lesion is not a cystic neoplasm but a large vascular complex. (c) Coronal magnetic resonance angiogram of the lower abdomen and pelvis shows that the lesion is a left-sided pelvic varix. Portal venous flow courses via the inferior mesenteric vein (IMV) into a complex knot of vessels in the left adnexal region (arrows).
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Figure 23c. Left-sided pelvic varix in a female patient with a palpable pelvic mass at physical examination. (a) Longitudinal US image of the pelvis shows a complex, multiseptated structure (arrows). (b) Longitudinal color Doppler image shows that the lesion is not a cystic neoplasm but a large vascular complex. (c) Coronal magnetic resonance angiogram of the lower abdomen and pelvis shows that the lesion is a left-sided pelvic varix. Portal venous flow courses via the inferior mesenteric vein (IMV) into a complex knot of vessels in the left adnexal region (arrows).
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Conclusions
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CT and CT angiography have become powerful tools for investigation of the liver. The addition of a portal-phase acquisition with 3D vascular reconstruction can augment the surgeon’s perception of potentially problematic varices by detailing the course of these tortuous vessels. This knowledge is important not only for major operations such as liver transplantation but for more common procedures in which an unexpected varix can result in significant bleeding. With this tool, the radiologist can significantly affect patient care and alert a colleague to potential disaster.
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Acknowledgments
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We thank Kari Pulfer for 3D reconstruction and Carrie Poole for manuscript preparation.
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Footnotes
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Abbreviations: SSD = shaded-surface display, 3D = three-dimensional
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References
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Abstract
LEARNING OBJECTIVES FOR TEST...
